PETROGRAPHY. 133 
Microscopic characters. Holocrystalline, microporphyritic, clathrate microfabric. Micro- 
phenocrysts: about 50 per cent, leucite, augite. Microgroundmass : about [60 per cent, augite, 
anorthite, olivine, magnetite, apatite, sometimes melilite and biotite. 
Anorthite. Groundmass: about 5 per cent, anhedral, interstitial, difficult to distinguish. 
Leucite. Microphenocrysts: about 30 per cent, 0.05 to 0.20 mm., subhedral to anhedral, 
equant, round sections, sometimes skeleton forms, inclusions common, very small, mostly of 
glass or augite, regularly arranged. 
Nephelite. Groundmass : about 5 per cent, anhedral, interstitial areas, difficult to detect. 
Augite. Microphenocrysts: about 20 per cent, o. 10 to 0.30 mm., anhedral, prismatic, or 
fragmentary, pale yellowish-gray, inclusions few. Microgroundmass: about 30 per cent, 0.02 
to 0.05 mm., anhedral, prismatic to equant, very pale yellowish-gray, arrangement partly 
tangential around the leucites. 
Olivine. Groundmass: 2 to o per cent, 0.05 to o. 10 mm., anhedral, equant. 
Biotite. i to o per cent, anhedral, small interstitial areas. 
Melilite. Groundmass : 3 to o per cent, anhedral, interstitial areas. 
Magnetite. Groundmass: about 2 per cent, o.oi to 0.05 mm., anhedral, equant. 
Apatite. About i per cent, 0.03 to 0.05 mm., subhedral, prismatic. 
Chemical composition and norm as on p. 131. 
Type specimen from Monte Rado, east of Lake Bolsena, Vulsinian District. 
III. 8. 2. 2. Saccal Albanose [Leucitite, Sacco Type]. 
Megascopic characters. In the hand specimen this type resembles closely that 
just described, being dense and very dark gray, and almost wholly aphyric, the very 
rare phenocrysts, when present, being of leucite and augite. In examining a series 
of specimens of the two, however, it is noticed that the color of the romal type is 
distinctly darker as a rule than that of the saccal, though both are so dark and 
aphanitic as to be called basalts in the field. 
Microscopic characters. To this type the description of the hernical braccianose 
applies very well, except as to the feldspar, which is here scarcely visible. The rock 
is holocrystalline and with the same xenomorphic granular fabric. There are fairly 
numerous microphenocrysts of augite, from 0.2 to 0.5 mm. long, in stout, subhedral 
prismoids and equant anhedral grains. They are of the usual pale-gray color, 
in some specimens with a zonal structure, slightly darker and greenish toward the 
center, and almost wholly free from inclusions. This augite has been studied by 
Viola,* though the variety examined by him is decidedly greener and apparently 
richer in the aegirite molecule than that shown in my sections. He gives the extinc- 
tion angle c At in the small non-pleochroic crystals as 45, while I obtained 42 for 
a A a- To this pyroxene he gives the name of fedorowite. As an analysis of typical 
augite from the rocks of the Roman Region was desirable, a specimen of this 
type was chosen for examination from near Ticchiena, north of Frosinone, in the 
Hernican District. The rock powder used for the chemical analysis of the rock was 
digested for some hours in warm dilute hydrochloric acid, to which a little hydro- 
fluoric acid was added. The residue was washed out with dilute solution of sodium 
carbonate and the process repeated, but without hydrofluoric acid, the final residue 
being, of course, washed perfectly free from all soluble salts. This process would 
* C. Viola, Neu. Jahrb., 1899, I, pp. 102-21. 
